Field of the Invention
The present subject matter relates generally to an apparatus and method for growing a diamond, and more specifically to an apparatus and method for growing a diamond using a plurality of heaters.
Related Art
The synthesis of diamond crystals by high temperature, high pressure processes via a temperature gradient method was established by the General Electric Company as described in U.S. Pat. No. 4,034,066. As a result of subsequent large-scale production by Sumitomo Electric Industries, Ltd., as described in U.S. Pat. No. 4,836,881, diamonds synthesized by this method are commercially available as heat sinks, super-precision cutting tools, and other fabricated products. The diamond growth process using a high temperature, high pressure apparatus can include a reaction cell which contains (a) graphite as a carbon source, (b) a diamond seed crystal, and (c) a solvent metal which separate the carbon source from the seed crystal.
During the growth of diamond crystals, the carbon source dissolves in solvent metal upon heating, and a temperature gradient exists between the carbon source and the seed crystal, thereby permitting diamond crystal to grow on seed crystal. The growth rate and the diamond quality depend not only on the applied temperature and pressure, but also on the alloy chemistry and core geometry. In addition, the growth rate strongly depends on the temperature gradient and difference between the dissolution site and growth site. As crystal growth continues, the positions of the materials shift and change. As a result, the temperature difference and gradient also changes, which result in either slowing down of the growth rate or incorporation of inclusions within the grown diamonds.
Conventional processes for growing diamonds adopted a single heater system which causes a fixed temperature gradient in the cell. One of the shortcomings of these systems is that the initial growth rate is higher than later growth rate due to the actual temperature gradient decreasing as the crystal grows. As the crystal reaches a certain size, growth will stop since no temperature gradient exists. Hence, according to the conventional method, in order to increase the productivity, the temperature gradient must be set as high as possible at the beginning. However, while this conventional method may increase the initial growth rate of diamond, this leads to another disadvantage, i.e., more inclusions incorporated in the diamond crystals. Thus, to grow high-quality yellow diamond crystals using a single heater, the growth rate is to be limited, which is normally below 6 mg per hour. But, for certain chemistries and geometries, it is ideal to start with a slow growth rate at the beginning to eliminate the inclusions, and increase the growth rate later on to increase productivity.